1. Field of the Invention
The present invention relates to an inkjet recording ink and ink cartridge, and recording process and recording apparatus that employ the ink respectively. Specifically, the present invention relates to an ink that provides superior image quality and high-speed printing ability in combination with plain paper, as well as storage stability and discharging stability, and an ink cartridge, recording process and recording apparatus that employ the ink respectively.
2. Description of the Related Art
Inkjet printers have been recently developing their market owing to their attracting features that printing is possible on plain paper, color printing is easily conducted, the size is miniaturized, the price is inexpensive, and the running cost is relatively low.
The typical properties demanded for the inkjet recording ink are those for achieving high image quality as tonality, image density, and bleeding; those for attaining reliability as dissolving or dispersing stability of colorant in the ink, storage stability of the ink, and discharging stability of the ink; those for assuring the reserving ability of recorded images as resistance to water and resistance to light; and those for accomplishing high-speed printing as rapid drying of ink. Various improvements have been proposed heretofore in order to realize these properties.
Traditionally, the colorants of the inkjet recording ink were mainly based on dyes owing to their superior coloring property and high reliability; recently, ink components containing pigments such as carbon blacks have been interested for the purpose to provide recorded images with resistance against light and water.
Further, the size of ink drops is going into smaller nowadays, therefore, the nozzle size is also going into smaller, in order to achieve higher image quality as well as higher speed printing.
However, it is considerably difficult to assure discharging stability when pigments are employed for the colorant and printers with smaller size of nozzles are utilized. As such, inkjet recording inks that satisfy these requirements with other necessary properties have not been developed yet.
Previously, for the purpose to enhance the reliability of printers, one way to solve the problem was to provide an ink composition that suppress the viscosity increase with time as low as possible. For example, Japanese Patent Application Laid-Open (JP-A) No. 2002-337449 discloses that suppressing the viscosity change of ink to less than ten times and the particle size change to less than three times, when the concentration of the ink is condensed to two times compared with beginning, result in the facts that the pigment coagulation may prevent the spread of ink and also may prevent the occurrences of the pore region on which ink is not printed. However, in the proposed ink, it is found to be difficult to form high quality images on plain paper.
Further, JP-A No. 2000-95983 discloses an ink, wherein the remainder after vaporizable ingredients in the ink are vaporized is still liquid, and the viscosity of the remainder is less than 10 times that of the beginning. However, the ink is based on dyes, the image quality on plain paper is relatively inferior even though the reliability is high.
Further, JP-A No. 09-111166 discloses an ink, wherein the viscosity of the remainder after moisture in the ink being vaporized at 60° C. is less than ten times that of prior to the vaporization. However, the ink is also based on dyes, the water resistance is insufficient, even though the reliability of ink and the durability of image quality are balanced through an addition of water-soluble polymer.
Further, JP-A No. 2001-262025 proposes that an ink with higher viscosity (5 to 15 mPa·s) is necessary to ensure high quality images. According to the proposal, the vaporizing rate should be adjusted at an initial period to assure reliability and specific compounds should be added as viscosity controller to adjust the viscosity. However, any description is not present concerning the particle size stability of the pigment to be employed, and the reliability is considered to be inferior when it is left to stand for a prolonged period in certain configuration and size of head and nozzle, although it is described that the reliability after 24 hours is assured.
As explained above, in order to assure high quality of printed images under relatively rapid printing velocity, inks with high viscosity are to be handled successfully, however, such inks with high viscosity are not able to be handled properly, since such inks are typically difficult to assure the reliability in the prior art.